This invention relates to manhole bases having sewer pipe connections sealed by gaskets between the sewer pipes and the manhole base.
Improvements have been made in manhole bases by lining the fluid conducting portions thereof. One example of such an improvement is described in U.S. Pat. No. 4,483,643 to Guggemos, which describes a canal bed shell having an open channel portion and pipe connecting portions. Unfortunately, edges of the channel portion and edges of the pipe connecting portions are exposed when installed in a manhole base and therefore, sewer fluids may ingress at the interface of the canal bed shell and a benching portion of the manhole base and ground water may ingress at the interface of the pipe connecting portion edges and the manhole base. Ingress of fluids in this manner can corrode the seating of the canal bed shell in the manhole base, ultimately destroying it. The manhole base can be refurbished by chipping out the canal bed shell but this can be difficult in bases where the entire benching and canal portions are lined.
In addition, the canal bed shell of the type described by Guggemos has fixed pipe connecting portions which extend through the circular wall of the manhole base and which are embedded in the concrete of the manhole base. Typically, these canal bed shells are embedded in the concrete at a factory and the entire base is shipped to the job site. The cost of shipping such bases can be quite expensive.
What would be desirable, is a manhole base which can be manufactured right at the job site and used to form a sewer system node which will resist the effects of groundwater pressure acting on the manhole base and which will resist corrosion of the manhole base under such conditions. In addition, there is a need for an on-site manufacturable manhole base which can connect to inlet and outlet sewer pipes which may be disposed at non-standard angles relative to the manhole base. The present invention addresses the above needs.